Abnormal Bias-Temperature Stress and Thermal Instability of <tex-math notation='LaTeX'>$\beta$ </tex-math>-Ga2O3 Nanomembrane Field-Effect Transistor

In this paper, we report on the electrical and thermal instability of β-Ga2O3 nanomembrane field-effect transistor with a bottom-gate configuration. The fabricated device exhibits high electrical performance of field-effect mobility of up to 60.9 cm2/V&#183;s, on/off-current ratio of 109 and subthreshold slope of 210 mV/dec. However, we observe abnormal positive threshold voltage (VTH) shifts under negative bias-temperature stress at an elevated operating temperature of 80 &#176;C as well as under temperature-dependent transfer characteristics up to 200 &#176;C. This abnormal instability is significantly influenced by the surface depletion effect, and is discussed using energy band diagram. The opposite VTH shift was achieved by applying atomic-layer deposited Al2O3 passivation layer.